Specific subgroups of the population bear a greater cancer burden than the general population. It has been hypothesized, and from our own prior studies we have preliminary evidence, that sexual minorities are among the population groups to experience cancer disparities. The lack of reliable population-based cancer data systems that include sexual orientation impedes the confirmation of the existence of cancer disparities due to sexual orientation. The main goal of this secondary data analysis is to link two California-specific data sources, cancer registry data and a statewide population-based survey that measured sexual orientation, to assess cancer disparities due to sexual orientation. Using county-level data on sexual orientation, we will test the hypothesis that geographic areas in which more sexual minorities (defined as self-identified gay, lesbian, bisexuals) are concentrated have higher breast, lung and colorectal cancer incidence, more advanced stage at diagnosis, and greater cancer mortality compared to areas with fewer sexual minorities. We have four specific aims to identify breast, lung and colorectal cancer disparities in California: 1. Examine the relationship of breast, lung, and colorectal cancer incidence to the area-specific percentage of sexual minority populations (defined as women or men who identify as lesbian, gay, or bisexual) in California counties. 2. Determine the rate of late stage breast and colorectal cancer diagnoses to the area-specific percentage of sexual minority populations (defined as women or men who identify as lesbian, gay, or bisexual) in California counties. 3. Compare breast, lung, and colorectal cancer mortality as a function of the area-specific percentage of sexual minority populations (defined as women or men who identify as lesbian, gay, or bisexual) in California counties. 4. Compare California counties on breast, lung, and colorectal cancer incidence, late stage diagnosis, and mortality as a function of Census-derived area-specific percentage of same-sex partnered households to area-specific estimates derived from self-reported sexual orientation information. To date, "true" population-based estimates of cancers in sexual minorities are not known, yet urgently needed. Our methodological approach can provide information about disparities due to sexual orientation in California, and provide for information to be later utilized to focus interventions. PUBLIC HEALTH RELEVANCE: Project Narrative Results from this study will show whether sexual minorities bear a disproportionate burden in California with respect to breast, lung, and colorectal cancers. If this innovative data use is successful, it can be replicated in other states, which also collect data on sexual orientation of their population and can ultimately be proposed as a useful tool for state health officials. In the absence of cancer surveillance data on sexual minorities, this tool can inform about within state disparities due to sexual orientation, and provide for information that can help focus interventions. Ultimately, this epidemiological approach to cancer disparities is a necessary first step on which we expect to build with follow-up research focused on understanding and eliminating disparities linked to sexual orientation.